In general, industrial furnaces are constructed to have three main sections, the tank at the lower portion of the furnace, the intermediate superstructure, and the crown positioned over the superstructure. In general, the tank and superstructure define a heating chamber. Supporting steel elements, such as channel irons for supporting the crown, and steel plates for supporting the superstructure sidewalls, function to allow the three main sections of the furnace to be independent of each other, thereby allowing separate maintenance on the three sections.
Heretofore, the conventional way to protect supporting steel members, especially the steel support plate extending over the tank and supporting the superstructure, from extreme heat has been to place refractory blocks called "tuckstones" on top of the support steel support plate, and the remaining refractory blocks that form the superstructure on top of the tuckstones. The prior art tuckstone generally is approximately L-shaped with a body portion that rests on the metal support plate and a nose portion which extends over and down in front of the metal support plate on the interior side within the furnace which protects the metal support plate from direct exposure to the extreme heat in the furnace. Replacement of the tuckstones is necessitated, especially in the case of continuous furnace campaigns, because of their susceptibility to thermal shock cracking, which eventually can lead to loss of the noses of the tuckstones, and hence loss of protection for the metal support plate. Such damage to the tuckstones and subsequent damage to the support plate can lead to reduced furnace life, or to expensive hot welding repairs of the metal support plate, or to the installation of expensive cooling coils adjacent the tuckstones which must be replaced as they deteriorate.
Inasmuch as the tuckstones are placed on top of the metal support plate, they form a part of the superstructure, and usually when the tuckstones are to be replaced they cannot be removed without removal of that portion of the superstructure which rests upon them. One example of a furnace structure is shown in U.S. Pat. No. 4,213,753 of Negroni et al wherein the tuckstones apparently support the superstructure.
The use of tuckstones having depending noses which extend over the inner edges of the horizontal metal support plate creates a tuckstone ledge or shelf which necessitates a step back superstructure within the furnace, thereby reducing furnace capacity, and the tuckstone ledge forms an area within the furnace where corrosive chemicals may be deposited, which in turn can contaminate the melt. These corrosive materials can be of particular concern in the case of glass furnaces. When, during operation of the furnace, the nose of a tuckstone breaks off the main body of the tuckstone and if the broken tuckstone is not replaced, flux line corrosion of the top rim of the tank sidewall can occur, thereby exposing the flux line (top surface of the melt) to direct flame contact which can reduce convection and reduce melt output per time unit. In addition, there will be an increase of energy consumption per melt unit.
It therefor can be seen that it would be desirable to provide a furnace construction wherein the tuckstones can be expediently removed, inspected and replaced, even when the furnace is hot.